1. Field of the Invention
This invention pertains to surgical procedures for stabilizing a spine. More particularly, this invention pertains to a novel surgical tool for use in such a procedure.
2. Description of the Prior Art
Chronic low back pain is one of the most common and perplexing problems facing the field of orthopedic surgery. In addition to the discomfort of the patient, low back pain has severe adverse societal impacts. Ineffective treatment of low back pain results in increased lost time from work and increased insurance claims. Much more tragic societal consequences arise from the patient's efforts to cope with chronic low back pain. These include loss of income or job, loss of self and family esteem, possible chronic dependence on drugs, alcohol and public relief programs.
In many cases, low back pain can be avoided if relative motion between spinal vertebra can be prevented. Immobilization (or, more commonly, intervertebral stabilization) is sought in a wide variety of treatment methods. To abate low back pain, stabilization is directed to stabilizing contiguous vertebra in the lumbar region of the spine.
While the following list is not exhaustive, it illustrates prior stabilization techniques:
1. Non-Surgical Stabilization
The simplest stabilization is accomplished through use of back braces. The brace is worn externally by the patient to restrict lumbar movement. Unfortunately, the brace is bulky and uncomfortable and limited in its effectiveness.
2. Surgical Stabilization
a. Generally
Low back pain is presently believed to be associated with anatomic changes in the discs which separate the lumbar vertebra. Surgical stabilization first identifies the degenerated disc and seeks to rigidly join the lumbar vertebra which are separated by the degenerated disc. Ideally, the surgery effectively replaces the vertebra-disc-vertebra combination with a single rigid vertebra. Various surgical techniques have developed which attempt to approach or approximate this ideal.
b. Anterior Spinal Interbody Fusion
The anterior route for fusion involves a surgeon seeking access to the spine through the front (i.e. stomach area) of the patient. Exposure of major organs and blood vessels is required. Accordingly, due to difficulty and danger, this method has not received wide-spread acceptance.
c. Posterior Interbody Fusion and Postero-Lateral Fusion
Posterior fusion means access to the spine is achieved through the back of the patient. Postero-lateral fusion is similar with access coming more from either or both sides of the patient. Several posterior or postero-lateral techniques are known.
i. Usual Single Level Postero-Lateral Fusion PA1 ii. Dowel-Type Interbody Fusion PA1 iii. Grafting Into A Cleaned Interbody Space PA1 iv. Need for Improved Techniques
The usual inter-traverse process fusion involves bone grafts connecting the transverse processes of contiguous vertebra. The transverse process are bone portions extending radially away from opposite sides of the vertebra body. The grafted bone is commonly taken from the iliac crest.
The inter-traverse process fusion has several drawbacks. Gross destruction of normal anatomy is required. Also, a significant incision is necessary to expose a sufficient area of the lumbo-sacral area in order to perform the surgery. This wide exposure results in high blood loss and significant muscle and bone destruction.
An additional drawback of this technique is that the fusion requires a significant time to become solid. For example, fusion may require nine to twelve months. During this period, the spine is rendered less stable that it was before the operation.
A further disadvantage of this technique is that the fusion occurs between the transverse processes which are spaced from the body of the vertebra. Accordingly, complete stability is not achieved.
A dowel technique for a posterior interbody fusion is known. In the dowel technique, a bore hole is formed through the degenerated disc area. The diameter of the bore is sized so that cutting takes place both into the disc and the opposing surfaces of the vertebra body. With the bore formed, bone dowels are placed within the bore. If successful, fusion occurs between the bone dowels and the opposing surfaces of the vertebra body.
The dowel-type technique is limited in effectiveness. The size of a bore which can be directly formed into the spine is limited by the access area to the spine. Namely, the vertebra structure, location of the spinal cord, location of important nerves and blood vessels restrict the effective maximum size of the bore which can be formed. As a result of this restriction, the amount of degenerative disc material which can be removed is limited. Also, the surface area of the vertebra body which is exposed and available for grafting is limited.
This technique requires removal of the degenerated disc. The degenerated disc is removed through chiseling or the like to clean the interbody space. When the interbody space is exposed, large bone segments are placed into the space and grafted to the opposing vertebra. This technique has enjoyed a high percentage of successful interbody fusions. However, the procedure is very difficult to perform requiring three to six hours by experienced surgeons. Also, the process of removing the disc exposes major nerves and blood vessels to damage. Due to the danger associated with this technique, it is in limited use.
As noted above, there are many techniques for stabilizing vertebra. However, these techniques have individual drawbacks. Due to the extreme economic and sociologic impact of chronic low back pain, a need for improved techniques with high effectiveness and decreased risks has long persisted and been sought in orthopedic surgery. However, techniques which meet the dual goal of high fusion with low acceptable risks have evaded the art.